U.S. patent application number 13/180431 was filed with the patent office on 2013-01-17 for appropriate led arrangement and power need in large-scale led display and lighting apparatus and method thereof.
This patent application is currently assigned to Chung-Yuan Christian University. The applicant listed for this patent is Cheng-Chih Chu, Guan-Chyun Hsieh. Invention is credited to Cheng-Chih Chu, Guan-Chyun Hsieh.
Application Number | 20130016496 13/180431 |
Document ID | / |
Family ID | 47518829 |
Filed Date | 2013-01-17 |
United States Patent
Application |
20130016496 |
Kind Code |
A1 |
Hsieh; Guan-Chyun ; et
al. |
January 17, 2013 |
Appropriate LED Arrangement And Power Need In Large-Scale LED
Display And Lighting Apparatus And Method Thereof
Abstract
Method for managing power of a display and apparatus thereof are
provided. The proposed method includes the following steps:
calculating a most appropriating voltage value and a most
appropriating current value form a plurality of LEDs; and obtaining
a first optimal working point according to the most appropriating
voltage value and the most appropriating current value, wherein the
first optimal working point is used for arranging the plurality of
LEDs.
Inventors: |
Hsieh; Guan-Chyun; (Chung Li
City, TW) ; Chu; Cheng-Chih; (Chung Li City,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hsieh; Guan-Chyun
Chu; Cheng-Chih |
Chung Li City
Chung Li City |
|
TW
TW |
|
|
Assignee: |
Chung-Yuan Christian
University
Chung Li City
TW
|
Family ID: |
47518829 |
Appl. No.: |
13/180431 |
Filed: |
July 11, 2011 |
Current U.S.
Class: |
362/97.1 ;
315/192; 362/227 |
Current CPC
Class: |
H05B 45/46 20200101 |
Class at
Publication: |
362/97.1 ;
362/227; 315/192 |
International
Class: |
G09F 13/04 20060101
G09F013/04; H05B 37/02 20060101 H05B037/02; F21S 4/00 20060101
F21S004/00 |
Claims
1. A method for managing a power source of a display, comprising a
plurality of light emitting diodes (LEDs) having a voltage value
and a current value, the method comprising steps of: calculating an
optimized voltage value and an optimized current value for the
display; and obtaining a first optimal working point for the
display according to the optimized voltage value and the optimized
current value.
2. The method as claimed in claim 1, further comprising steps of:
using a square root of a total number of the plurality of LEDs to
determine a first reference value being one of a floor value and a
ceiling value of the square root; and arranging the plurality of
LEDs as a first plurality of parallel connected LED cascades
according to the first optimal working point, and a total number of
the first plurality of parallel connected LED cascades of the
plurality of LEDs equals to the first reference value, wherein a
total number of serially connected LEDs in each of the first
plurality of parallel connected LED cascades equals to the first
reference value.
3. The method as claimed in claim 2, further comprising steps of:
using a square root of the first reference value to determine a
second reference value being one of a floor value and a ceiling
value of the square root thereof; obtaining a second optimal
working point according to the optimized voltage value and the
optimized current value; arranging a second plurality of parallel
connected LED cascades according to the second optimal working
point; and connecting the first plurality of LED cascades to the
second plurality of parallel connected LED cascades, wherein a
total number of serially connected LEDs in each of the second
plurality of parallel connected LED cascades equals to the second
reference value.
4. The method as claimed in claim 1, further comprising a step of
obtaining a k-th optimal working point, wherein k is a positive
integer.
5. The method as claimed in claim 4, further comprising steps of:
using a power of 1 2 k ##EQU00012## of the total number of the
plurality of LEDs (N), to determine a k-th reference value being
one of a floor value and a ceiling value of the power of 1 2 k
##EQU00013## of N; arranging a k-th plurality of parallel connected
LED cascades according to the k-th optimal working point; and
connecting a (k-1)th plurality of LED cascades to the k-th
plurality of parallel connected LED cascades, wherein a total
number of parallel connected k-th LED cascades equals to a positive
integer being one of a floor value and a ceiling value of a power
of m = 1 k 1 2 m ##EQU00014## of N, and a total number of serially
connected LEDs in each of the k-th plurality of LED cascades equals
to the k-th reference value.
6. The method as claimed in claim 1, wherein the required voltage
for operating each of the plurality of LEDs is essentially 3.5
volts.
7. The method as claimed in claim 1, wherein the method is
implemented by one being selected from a group consisting of a
notebook, a mobile device and a lighting device.
8. A backlight device having a plurality of LEDs, comprising: a
plurality of parallel connected LED cascades having N LEDs, wherein
N is a positive integer, and a total number of the plurality of
parallel connected LED cascades being one of a floor value and a
ceiling value of a square root of N; and a total number of serially
connected LEDs in each of the plurality of parallel connected LED
cascades equals to a positive integer being one of a floor value
and a ceiling value of the square root of N.
9. A backlight device having a plurality of LEDs, comprising: a
plurality of parallel connected LED cascades having N LEDs, wherein
N is a positive integer, and a total number of the plurality of
parallel connected LED cascades equals to a positive integer being
one of a floor value and a ceiling value of a square root of N.
10. A lighting apparatus having a plurality of LEDs, comprising: a
plurality of parallel connected LED cascades having N LEDs, wherein
N is a positive integer, and a total number of serially connected
LEDs in each of the plurality of parallel connected LED cascades
equals to a positive integer being one of a floor value and a
ceiling value of a square root of N.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of the conference paper
entitled "AN APPROPRIATE ARRANGEMENT OF MULTIPLE LEDS FOR OPTIMAL
POWER NEED" in 12th Intl Symp. Science and Technology of Light
Sources and 3.sup.rd Intl Conf. White LED and Solid State Lighting,
pp. 221-222, Netherlands, Jul. 11-16, 2010, which is incorporated
by reference as if fully set forth herein.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of managing power
of a plurality of light emitting diodes (LEDs), in particular to
the method of arranging the ways of connecting LEDs in parallel and
in serial in displays.
BACKGROUND OF THE INVENTION
[0003] Aiming at energy-saving and mercury-free environmental
requirements, LED technologies have become the most important
lighting source applied in large-scale LCD panels or lighting
apparatuses. Based on thermal consideration, the LED rated power
below 1 Watt even lower than 0.1 Watt has been the major cell
device applied in nowadays displays or lighting apparatuses. A
large amount, hundreds even thousands, of LEDs are necessary to be
arranged in an apparatus and their connections are mostly in serial
and/or in parallel forms. However, the combination form and the
power demand for LEDs are very closely related to each other in
design consideration. Therefore, the power demand for operating
LEDs is highly related to the arrangement of LEDs.
[0004] A very high voltage is required if a large amount of LEDs
are merely serially connected in one string, where a much larger
current is required if the LEDs are only connected in parallel
strings. As a result, it is necessary for a power supply to be
configured with very high (low) output voltage and with very low
(high) current source if all LEDs are connected only in serial or
in parallel.
[0005] In other words, improper combination may raise the
difficulty of the power design for driving multiple LEDs
(multi-LEDs). Moreover, a large amount of LEDs connected only in
either serial or parallel form may increase the probability of
failure when operating LED devices and raise the difficulty for
designing power supplies, and causing thermal issues as well. In
fact, the above-mentioned issues are difficult to be solved by
simply biasing the multi-LEDs in a stable operation region. A
preferred biasing strategy for such as transistor, diode, and even
power LEDs, is to place the operating point around the intermediate
portion of the power dissipation (PD) curve to gain excellent
performance. However, most literatures focus only on the promotion
of LED drive configurations and are lack of investigation on the
mentioned issues, even the estimation of power need is also scarce
and scattered.
[0006] Therefore, an advanced method for solving the
above-mentioned issues is highly needed.
SUMMARY OF THE INVENTION
[0007] The present application utilizes a widely used mean-value
approach, which is much closer to the practical problems, to find a
proper bias operating point of the multi-LEDs, and then to
determine an appropriate combination and power need for determining
the LED arrangement and power supply design, respectively.
[0008] Besides, the present application also explores a simple LED
layout strategy to prevent from possible electromagnetic
interference and overloading in voltage. Finally, a design example
implementing a LED backlighting display for a 20 inches TV verifies
the feasibility of the proposed method.
[0009] According to the first aspect of the present invention, a
method for managing a power source of a display, comprising a
plurality of light emitting diodes (LEDs) having a voltage value
and a current value, comprises steps of: calculating an optimized
voltage value and an optimized current value for the display; and
obtaining a first optimal working point for the display according
to the optimized voltage value and the optimized current value.
[0010] According to the second aspect of the present invention, a
backlight device having a plurality of LEDs comprising a plurality
of parallel connected LED cascades having N LEDs, wherein N is a
positive integer, and a total number of the plurality of parallel
connected LED cascades being one of a floor value and a ceiling
value of a square root of N, and a total number of serially
connected LEDs in each of the plurality of parallel connected LED
cascades equals to a positive integer being one of a floor value
and a ceiling value of the square root of N.
[0011] According to the third aspect of the present invention, a
backlight device having a plurality of LEDs comprises a plurality
of parallel connected LED cascades having N LEDs, wherein N is a
positive integer, and a total number of the plurality of parallel
connected LED cascades equals to a positive integer being one of a
floor value and a ceiling value of a square root of N.
[0012] According to the fourth aspect of the present invention, a
lighting apparatus having a plurality of LEDs comprises a plurality
of parallel connected LED cascades having N LEDs, wherein N is a
positive integer, and a total number of serially connected LEDs in
each of the plurality of parallel connected LED cascades equals to
a positive integer being one of a floor value and a ceiling value
of a square root of N.
[0013] Other objects, advantages and efficacy of the present
invention will be described in detail below taken from the
preferred embodiments with reference to the accompanying drawings,
in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a diagram illustrating the proposed PD curve of
the LEDs and the first deduction of finding their appropriate
operating point for the estimation of combination and power need
according to the present invention;
[0015] FIG. 2A is a diagram illustrating that the LEDs are
connected in one series according to the present invention;
[0016] FIG. 2B is a diagram illustrating that the LEDs are parallel
connected in two series according to the present invention;
[0017] FIG. 2C is a diagram illustrating that the LEDs are parallel
connected in N series according to the present invention;
[0018] FIG. 3 is a diagram illustrating the process to find the
appropriate operating point of multi-LEDs for estimating the
combination and the power need, including the first and second
deductions;
[0019] FIG. 4A is a diagram illustrating that N LEDs are originally
connected in one series;
[0020] FIG. 4B is a diagram illustrating the estimated combinations
of N LEDs for arrangement after the first deduction;
[0021] FIG. 4C is a diagram illustrating the estimated combinations
of N LEDs for arrangement after the second deduction; and
[0022] FIG. 5 is a diagram illustrating an exemplary circuit scheme
for driving multi-LEDs in a 20' LED TV panel.
[0023] Throughout the figures, the same reference numerals and
characters, unless otherwise stated, are used to denote like
features, elements, components or portions of the illustrated
embodiments. Moreover, while the subject disclosure will now be
described in detail with reference to the figures, it is done so in
connection with the illustrative embodiments. It is intended that
changes and modifications can be made to the described embodiments
without departing from the true scope and spirit of the subject
disclosure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] The present invention will now be described more
specifically with reference to the following embodiments. It is to
be noted that the following descriptions of preferred embodiments
of this invention are presented herein for purposes of illustration
and description only; it is not intended to be exhaustive or to be
limited to the precise disclosed form.
[0025] First of all, we establish a PD curve of multi-LEDs on i-v
plane to describe their power behavior. An average conductance g,
of multi-LEDs derived between the two rated end points of the PD
curve is then moved in a direction that translates the PD curve to
a tangent point, where the appropriate operation point of the
multi-LEDs is located. In addition, a general deduction process to
further find an appropriate LED arrangement as well as the power
need is also presented. An estimation of finding an appropriate
combination for large amount of the LEDs can then be easily
acquired by simply taking multiple square roots of the number of
LEDs after multiple deductions. The necessary times for deduction
depend on whether the estimated LED arrangement is suitable for
power supply design.
[0026] In general, the consideration for well biasing an individual
LED is to place the operating point around the middle portion of
the maximum power dissipation (PD) curve and not over the
safe-operating area (SOA). However, the bias idea of multi-LEDs is
basically the same as that of individual LED. We first define
multi-LEDs as N LEDs, where N is an integer. Based on the device
characteristic, we can easily describe the PD curve of the N LEDs
on i-v axis as shown in FIG. 1. Interestingly, all LEDs connected
in series and those connected in parallel can be easily found at
the two rated ends of the proposed PD curve in FIG. 1. Accordingly,
the power dissipation P.sub.D of N LEDs on i-v plane can then be
described by
P D = NV D I D .ident. V ma x I m i n ( 1 ) ##EQU00001##
for all connected in series, or
P D = NI D V D .ident. I ma x V m i n ( 2 ) ##EQU00002##
for all connected in parallel. Where V.sub.D and I.sub.D are
respectively the forward voltage and current of an individual LED,
and we define V.sub.max=NV.sub.D, V.sub.min=V.sub.D,
I.sub.max=NI.sub.D, and I.sub.min=I.sub.D.
[0027] Both Eq. Eqs. (1) and (2) are equivalent to each other in
this case. The proposed PD curve of multi-LEDs depicted in FIG. 1
is basically valid under the rated power of SOA. The case on PD
curve of maximum rated current at I.sub.max=NI.sub.D with minimum
parallel string voltage V.sub.min=V.sub.D is exactly the situation
of all LEDs connected in parallel. On the other hand, that of the
maximum rated voltage V.sub.max=NV.sub.D with minimum string is
exactly for all LEDs connected in series. Accordingly, the possible
combination in series and/or in parallel can be easily acquired
along the PD curve by changing the integer N. If an intuitive
bisection method conducts, the combination in series and/or in
parallel can be easily established as shown in FIG. 2A-2C, which is
usual cases of guessing design strategy.
[0028] In fact, the LED arrangement and power need are tightly
related each other, which significantly concerns the power supply
design and the operation situation of multi-LEDs for uniformly
producing luminous output as expected. Therefore, how to estimate
appropriate combination of multi-LEDs for arrangement as well as to
match the power need for power supply design is quite an important
issue in a large-scale LED display.
[0029] Modeling by mean-value approach Basically, the PD curve of N
LEDs as proposed in FIG. 1 can be easily achieved by referring to
the rated power from manufacture. The current i of the N LEDs in
terms of voltage v along the PD curve on i-v plane can be obtained
by
i = f ( v ) = P D v ( 3 ) ##EQU00003##
If f(v) in FIG. 1 is continuous in [V.sub.min, V.sub.max] and
differentiable in (V.sub.min, V.sub.max), there exists some point
v.sub.c.epsilon.(V.sub.min,V.sub.max) such that
f(V.sub.max)-f(V.sub.min)=(v.sub.c)(V.sub.max-V.sub.min) (4)
From Eq. (3), yield
f ' ( v c ) = - P D v c 2 and ( 5 ) v c 2 = P D V ma x - V m i n I
ma x - I m i n = V ma x V m i n ( 6 ) ##EQU00004##
It is obtained that
v.sub.c.ident.V.sub.opt= {square root over (V.sub.maxV.sub.min)}
(7)
where v.sub.c=V.sub.opt is the optimal voltage. The optimal current
I.sub.opt can then be given, from Eqs. (1) and (7), by
i.sub.c.ident.I.sub.opt= {square root over (I.sub.maxI.sub.min)}
(8)
[0030] The average conductance g.sub.av of multi-LEDs can be easily
given by plotting a line between the two rated ends of the PD curve
under SOA, that is
g av = m .ident. - I ma x - I m i n V ma x - V m i n ( 9 )
##EQU00005##
where g.sub.av defined is equivalent to a slope m.
[0031] In Eq. (9), the minus sign means the conductance descends
along the PD curve when the operating current decreases and voltage
increases, and vice versa, which basically should comply with
P.sub.D=NV.sub.DI.sub.D. If we try to move the average conductance
line g.sub.av in a direction that parallels the tangent line of the
PD curve at a point c with slope m as the green line in FIG. 1, the
appropriate operation point of N LEDs given by (i.sub.c,
v.sub.c)=(V.sub.opt, I.sub.opt) is then obtained from Eqs. (7) and
(8). Accordingly, this operation point c contributes the
appropriate estimation in combination and power need for the
multi-LEDs to be arranged. We define the arrangement of LEDs after
estimation consists of q parallel strings and each string has p
LEDs in series connection. From Eqs. (7) and (8), we then have the
required power need from the estimated operation point given by
V.sub.opt= {square root over (V.sub.maxV.sub.min)}.ident.pV.sub.D
(10)
and
I.sub.opt= {square root over (I.sub.maxI.sub.min)}.ident.qI.sub.D
(11)
[0032] Interestingly, from Eqs. (1), (2), (10) and (11), we then
have a simple and compact expression for the estimated combination
of multi-LEDs, that is,
p=q= {square root over (N)} (12)
[0033] Eq. (12) intuitively shows the easy estimation by simply
taking the square root of the total number of N LEDs to be
arranged. Especially, the number of parallel strings is certainly
the same as those of series strings, which indeed simplifies the
design idea developed in this brief.
[0034] Generalized Approach to Optimal Arrangement If much larger
amount of LEDs is to be arranged in a display panel, the estimation
from Eqs. (10) and (11) for such point c in FIG. 1 may not fully
satisfy the design consideration due to probable difficulty in
power design after the first derivation. This situation may occur
due to the estimated serial string voltage of LEDs is still so
high. Therefore, a further estimation for continuously finding
another combination suitable for power design is necessary. The
continuous estimation process can be seen in FIG. 3, in which only
two deduction processes are explored for instance. The second
deduction for finding the second operating point (V.sub.opt2,
I.sub.opt2) on i-v coordinate is easily conducted by only
considering the first estimated optimal point (V.sub.opt1,
I.sub.opt1). That is, the first derived string voltage and parallel
current, and the point (V.sub.max1, I.sub.min1). In other words,
only points between c.sub.1 and a on the PD curve are considered as
the design references during the second deduction. It should be
noted that the operating point a at (V.sub.max1,
I.sub.min1)=(NV.sub.D, I.sub.D) in FIG. 3 is exactly the point
(V.sub.max, I.sub.min)=(NV.sub.D, I.sub.D) in FIG. 1.
[0035] Additionally, the point a on PD curve in FIG. 3 always
remains unchanged regardless of multiple deduction processes. In
FIG. 3, the second deduction process for fording the second average
conductance g.sub.av2 and the slope m.sub.2 is the same as that in
the first deduction. By utilizing the mean-value approach with
trigonometric translational method, the g.sub.av2 line tangential
to point c.sub.2 of the PD curve gives the second optimal point at
(V.sub.opt2, I.sub.opt2) on i-v plane. The generalizing derivation
for kth deduction referred to FIG. 3 can be described as
follows.
V.sub.max,k=p.sub.kV.sub.D (13)
V.sub.min,k=V.sub.D (14)
I.sub.max,k=q.sub.kI.sub.D (15)
and
I.sub.min,k=I.sub.D (16)
where k.quadrature.1. With reference to Eqs. (10)-(12), we can find
the k-th optimum point for voltage and current.
V.sub.opt,k= {square root over
(V.sub.max,kV.sub.min,k)}=p.sub.kV.sub.D (17)
and
I.sub.opt,k= {square root over
(I.sub.max,kI.sub.min,k)}=q.sub.kI.sub.D=p.sub.kI.sub.D (18)
where p.sub.k=q.sub.k is the same as the Eq. (12) of the first
derivation. From Eqs. (12), (17) and (18), we have
p k = N 1 2 k ( 19 ) ##EQU00006##
for k.quadrature.1.
[0036] Eq. 19 gives the k-th combination for arranging
N=(p.sub.k).sup.2k LEDs. In other words, there have {square root
over (N)} parallel strings and each series string has {square root
over (N)} LEDs in the first deduction. Entering the second
deduction, each of parallel strings is further partitioned into
{square root over (N)} sub-parallel strings and each sub-series
string has {square root over (N)} LEDs. In other words, we then
have total of {square root over (N)} {square root over (N)}
sub-parallel strings and each sub-series string has {square root
over (N)} LEDs after the second deduction. Possibly going on the
subsequent deduction process depends on whether the estimated
sub-string voltage reaches the proper power need for power design.
Thus, the total number of the parallel strings Q.sub.k after the
kth deduction will be
Q k = N 1 2 N 1 4 N 1 6 N 1 2 k = N k = 1 .infin. 1 2 k ( 20 )
##EQU00007##
and the kth series string always has the number of LEDs the same as
the Eq. (19).
[0037] FIG. 4A shows that N LEDs are originally connected in one
series. The estimated combination of N LEDs after the first
deduction is shown in FIG. 4B, and the estimated combination of N
LEDs after two deductions for example is realized in FIG. 4C, in
which the estimated parallel strings are
q.sub.11+q.sub.12+q.sub.13+ . . . for the first deduction, and then
q.sub.11 will partition into q.sub.211+q.sub.212+q.sub.1213+ . . .
, and q.sub.12 into q.sub.221+q.sub.222+q.sub.223+ . . . , . . .
and so on after the second deduction. Finally, the total
2nd-estimated parallel strings in this example will be N.sup.3/4
from Eq. (20) and each 2.sup.nd-estimated series string has LEDs of
N.sup.1/4 from Eq. (19), where N is the number of LEDs to be
arranged.
[0038] If much more quantity of sub-parallel strings estimated is
required after multiple deductions, increasing power modules in
parallel to share the large current request is feasible in design
consideration. In practice, the required deduction would be no more
than two to four times since the estimation is simply counted by
taking square root of the number of LEDs.
[0039] Eq. 19 gives a general estimation to determine the number of
LEDs in the kth-estimated series string by simply taking k square
roots through the kth deduction, in which the total number of the
parallel strings is given in Eq. 20. The appropriate power need can
be easily estimated for power design according to the kth operating
point of the multi-LEDs given from Eqs. 17 and 18. In practice, we
first check whether the estimated string voltage is suitable for
power design after the first deduction. If not, a further deduction
should continuously conduct until the power need reaches the proper
power design reference. If the estimated string voltage is still so
high then further deduction is necessary until reaching a suitable
requirement for design.
[0040] However, if many parallel strings are required after
multiple deductions, such as shown in FIG. 4C for example, much
large current request in power design may be necessary. In this
situation, increasing multiple power modules in parallel for
current sharing are the way in design consideration. Moreover, it
is quite important for LED layout to avoid LED fault and prevent
interference between series and parallel strings during
arrangement. Additionally, an interlacing arrangement in layout is
suggested to reduce the electromagnetic interference and possible
LED fault between the neighboring strings.
[0041] An exemplary design of the present invention is shown in
FIG. 5. A LED display for a 20 inch LCD TV with area of 41
cm.times.31 cm=1271 cm.sup.2 is designed to be fulfilled about 600
LEDs, in which each white LEDs has rated current 25 mA and rated
power P.sub.D=110 mW. After calculation in real area of the
display, the possible quantity of LEDs to be used is 588. The white
LED in normal condition has forward voltage V.sub.D=3.5V and
current I.sub.D=20 mA. The relative parameters for the 588 LEDs in
this design are respectively estimated as follows:
From Eq. (1), the maximum power dissipation is given by:
P.sub.D=3.5V.times.0.02A.times.588=41.16W (21)
[0042] For all LEDs connected in series, we have
V.sub.max=3.5V.times.588=2058V (22)
and
I.sub.min=20 mA (23)
For all LEDs connected in parallel, we have
V.sub.min=3.5V (24)
and
I.sub.max=20 mA.times.588=11.76A (25)
The PD curve of the 588 LEDs can then be easily plotted with
reference to FIG. 1 according to Eqs. (21)-(25). From Eqs. (7) and
(8), after the first deduction, we can easily find the optimal
operating point for the total 588 LEDs, i.e.,
V opt = V m i n .times. V ma x = 3.5 .times. 588 .times. 3.5 =
84.87 V and ( 26 ) I opt = I m i n .times. I ma x = 20 .times. 588
.times. 20 = 484.97 mA ( 27 ) ##EQU00008##
From Eq. (9), we have the average conductance g.sub.av=5.63 mS at
(V.sub.opt, I.sub.opt) on the PD curve of i-v plane. The number of
parallel strings q and p LEDs in each series string can then be
respectively estimated by, from Eqs. (10) and (11),
p=84.87V/3.5V.apprxeq.24.25 (28)
and
q=484.97 mA/20 mA.apprxeq.24.25 (29)
[0043] Both p and q are equivalent to meet Eq. (12). Since the
estimated power need in Eqs. (26) and (27) are suitable for power
design, no further deduction is required in this design. In
realization, if we employ 24 parallel strings and each string has
24 LEDs in series, there will be lack of 12 LEDs for
arrangement.
[0044] However, a minor modification conducts in this design using
24 LEDs in series for twelve series strings and 25 LEDs in series
for another twelve strings, in which total parallel strings are
still kept as 24. Thus in all, we have 24.times.12+25.times.12=588
LEDs completely meeting the specification. This approach will make
the string voltage difference within 3.5V between all 24 strings of
LEDs, which can be compensated in power supply design. From Eqs.
(26) and (27), a 48 W boost converter with V.sub.i=12V.sub.dc,
V.sub.out=96V.sub.dc, I.sub.o=0.5 A, and switching frequency
f.sub.s=50 kHz is designed and implemented. In order to ensure the
capacity of the power supply afford to meet the estimated string
voltage of 88V.sub.dc, the output voltage up to 96V.sub.dc and
output power of 48 W with 10% of tolerant capacity is considered.
Moreover, the suggested implementation as shown in FIG. 6 outlines
in parallel with 24 current sink circuits supplied by a constant
voltage source estimated as 96V.sub.dc. The above illustrated
experiment shows excellent performance for the multi-LEDs biasing
with the estimated power supply to produce almost uniform luminous
output in the display during a wide-range dimming process, and a
linear current regulator is employed as current sink circuit for
current balance among all strings.
[0045] Since the output voltage of the designed power supply has
10% of tolerant capacity, the current sink circuit can then
regulate itself against the voltage variation of the string LEDs,
the currents in 24 strings are almost close to each other. All LEDs
in the display panel can produce almost equal luminous output
during a wide-range dimming from dark to 550 cd/m.sup.2 measured at
50 cm. The experimental setup for realizing the proposed strategy
and evidencing its feasibility is shown in FIG. 7.
[0046] To sum up, in the present invention, an appropriate
combination and power need for large amount of LEDs arranged in a
display is estimated by simply taking the square root of the number
of LEDs. Moreover, a general estimation for much large amount of
LEDs is also achieved by simply taking multiple square roots of the
number of LEDs. Implementing consideration for harmonizing the
estimated parameters, such as the LED arrangement, power design,
and current balance, are clearly explored in the practical example.
A design example for a typical 20' LED TV display with 588 LEDs is
examined for verifying the feasibility of the proposed strategy.
Experimental result evidences the proposed strategy enables the
large amount of LEDs biased at a well operating state and almost
producing equally luminous output in the display from dark to 550
cd/m.sup.2 measured at 50 cm during a wide-range dimmer
control.
Embodiments
[0047] 1. A method for managing a power source of a display,
comprising a plurality of light emitting diodes (LEDs) having a
voltage value and a current value, the method comprising steps
of:
[0048] calculating an optimized voltage value and an optimized
current value for the display; and
[0049] obtaining a first optimal working point for the display
according to the optimized voltage value and the optimized current
value.
[0050] 2. The method as claimed in Embodiment 1, further comprising
steps of:
[0051] using a square root of a total number of the plurality of
LEDs to determine a first reference value being one of a floor
value and a ceiling value of the square root; and
[0052] arranging the plurality of LEDs as a first plurality of
parallel connected LED cascades according to the first optimal
working point, and
[0053] a total number of the first plurality of parallel connected
LED cascades of the plurality of LEDs equals to the first reference
value, wherein a total number of serially connected LEDs in each of
the first plurality of parallel connected LED cascades equals to
the first reference value.
[0054] 3. The method as claimed in Embodiment 1 or 2, further
comprising steps of:
[0055] using a square root of the first reference value to
determine a second reference value being one of a floor value and a
ceiling value of the square root thereof;
[0056] obtaining a second optimal working point according to the
optimized voltage value and the optimized current value;
[0057] arranging a second plurality of parallel connected LED
cascades according to the second optimal working point; and
[0058] connecting the first plurality of LED cascades to the second
plurality of parallel connected LED cascades, wherein a total
number of serially connected LEDs in each of the second plurality
of parallel connected LED cascades equals to the second reference
value.
[0059] 4. The method as claimed in anyone of the above-mentioned
Embodiments, further comprising a step of obtaining a k-th optimal
working point, wherein k is a positive integer.
[0060] 5. The method as claimed in anyone of the above-mentioned
Embodiments, further comprising steps of:
[0061] using a power of
1 2 k ##EQU00009##
of the total number of me plurality of LEDs (N), to determine a
k-th reference value being one of a floor value and a ceiling value
of the power of
1 2 k ##EQU00010##
of N;
[0062] arranging a k-th plurality of parallel connected LED
cascades according to the k-th optimal working point; and
[0063] connecting a (k-1)th plurality of LED cascades to the k-th
plurality of parallel connected LED cascades, wherein a total
number of parallel connected k-th LED cascades equals to a positive
integer being one of a floor value and a ceiling value of a power
of
m = 1 k 1 2 m ##EQU00011##
of N, and a total number of serially connected LEDs in each of the
k-th plurality of LED cascades equals to the k-th reference
value.
[0064] 6. The method as claimed in anyone of the above-mentioned
Embodiments, wherein the required voltage for operating each of the
plurality of LEDs is essentially 3.5 volts.
[0065] 7. The method as claimed in anyone of the above-mentioned
Embodiments, wherein the method is implemented by one being
selected from a group consisting of a notebook, a mobile device and
a lighting device.
[0066] 8. A backlight device having a plurality of LEDs,
comprising:
[0067] a plurality of parallel connected LED cascades having N
LEDs, wherein N is a positive integer, and a total number of the
plurality of parallel connected LED cascades being one of a floor
value and a ceiling value of a square root of N; and
[0068] a total number of serially connected LEDs in each of the
plurality of parallel connected LED cascades equals to a positive
integer being one of a floor value and a ceiling value of the
square root of N.
[0069] 9. A backlight device having a plurality of LEDs,
comprising:
[0070] a plurality of parallel connected LED cascades having N
LEDs, wherein N is a positive integer, and a total number of the
plurality of parallel connected LED cascades equals to a positive
integer being one of a floor value and a ceiling value of a square
root of N.
[0071] 10. A lighting apparatus having a plurality of LEDs,
comprising:
[0072] a plurality of parallel connected LED cascades having N
LEDs, wherein N is a positive integer, and a total number of
serially connected LEDs in each of the plurality of parallel
connected LED cascades equals to a positive integer being one of a
floor value and a ceiling value of a square root of N.
[0073] While the invention has been described in terms of what is
presently considered to be the most practical and preferred
embodiments, it is to be understood that the invention needs not be
limited to the disclosed embodiments. Therefore, it is intended to
cover various modifications and similar configuration included
within the spirit and scope of the appended claims, which are to be
accorded with the broadest interpretation so as to encompass all
such modifications and similar structures.
* * * * *